This invention relates generally to direct current machines, and, more specifically, to a control apparatus for regulating machine armature current and field current in accordance with machine efficiency computed in real time to obtain maximum machine efficiency irrespective of machine load conditions.
Direct current machine drive systems are commonly employed in various industrial applications requiring adjustable machine speed. Typically, a direct current machine drive system comprises a direct current machine and a pair of adjustable direct current power supplies, one for supplying machine armature current, the other for supplying machine field current. Usually each of the pair of adjustable direct current power supplies comprises either a phase controlled rectifier circuit or a chopper circuit whose output voltage can be varied by varying phase controlled rectifier or chopper circuit conduction, respectively, thereby permitting machine armature current and machine field current to be adjusted accordingly.
Heretofore, control apparatus employed to regulate machine drive system armature current and field current operated to obtain maximum machine efficiency by varying armature current in accordance with a predetermined relationship between armature current and machine air gap flux. Such operation is premised on the assumptions that: (1) machine torque is uniquely related to machine speed; (2) machine armature and field resistances are constant and independent of temperature; and (3) machine voltages and currents contain no harmonics. Regretably, such ideal conditions hardly ever exist during operation of a conventional direct current machine drive system and therefore, optimum machine efficiency is virtually never obtained by use of such prior art control apparatus.
In contrast, the control apparatus of the present invention obtains optimum machine efficiency by regulating machine armature current and machine field current responsive to optimum machine armature current and optimum machine air gap flux, respectively, which are determined in accordance with machine efficiency computed in real time.